Reactance transformer



NOV. 15, 1938. J, 3, SOLA 2,136,895

REACTANCE TRANSFORMER Filed Aug. 27. 1935 PUSH - Ea 2 5 24 a; m a? f m-W NH Wm. w n

Patented Nov. 15, 1938 UNITED STATES PATENT OFFICE 7 Claims.

My invention relates to reactance transformers for use with neon or other luminous tubes and of the type employing a plurality of secondary coil sections grounded to the core at their mid-point,

and it has for its object the provision of a new and improved form and arrangement of parts by reason of which the current through the secondary windings is kept from increasing beyond a predetermined safe maximum when a short-circuit leakage takes place around one of the secondary coil sections, as when one of the secondary terminals is shorted to the transformer core upon breakage of a neon tube, or otherwise. It is one of the objects of my invention to provide an improved arrangement of this type by which a shunt path is provided which shall be efiective, when one of the secondary coils is short-circuited, for diverting a substantial portion of the flux from the portion of the core on which said secondary coil section is mounted so as to prevent the establishment of an induced current in said coil section of such strength as to burn out the coil or otherwise injure the coil or its insulation.

It is another object of my invention to improve devices of this type in sundry details hereinafter pointed out. The preferred means by which I have accomplished my several objects are illustrated in the drawing and are hereinafter specifically described. That which I believe to be new and desire to cover by Letters Patent is set forth in the claims.

In the drawin Fig. 1 is a diagrammatic top face view of my improved transformer;

Fig. 2 is a cross sectional view taken at line 22 of Fig. 1;

Fig. 3 is a view similar to Fig. l but showing a modified form of construction; and

Fig. 4 is a cross sectional view taken at line 4-4 of Fig. 3.

Referring now particularly to Figs. 1 and 2 of the drawing, indicates a laminated core in the form of a loop comprising side bar portions H and i2 formed integrally with a cross leg portion l3 and a cross leg portion [4 having a snug tongue and groove connection with the ends of the side bar portions II and I2. Primary coil means comprising coil sections I5 and I6 mounted upon the side bar portions H and I2 respectively and connected in cooperative relation with respect to each other is mounted upon the core l0. Secondary coil means is also mounted upon the core loop, comprising coil sections l1 and I8 mounted upon the side bar portions l I and 12 in end to end relation to the primary coil sections l5 and [6 respectively, such secondary coil sections being connected in cooperative relation with respect to each other.

Across the core-loop between the primary coil means and the secondary coil means, I have provided auxiliary core means in the form of a laminated bar l9 which serves as a shunt path for a portion of the flux diverted from the portion of the core loop upon which the secondary coil sections are mounted. Two air gaps of equal effective width are provided in spaced relation to each other between the side bars I l and I2 through the shunt connection provided by the bar I9, such air gaps in the arrangement shown being provided at the ends of the bar H? at the points 20 and 2!. The'bar I9 is connected in the arrangement shown with the cross leg M of the loop by an auxiliary core bar 22 which in the arrangement shown is formed integrally with the bar l9 and also integrally-with the cross leg portion M, the core bar portion 22 being of the same cross-seetional size in the arrangement shown as that of the core bar portion l9. As is shown inFig.2,tlie auxiliary core bar 22 is in laminated form, as are all the parts of the core structure as shown in Fig. 1. As is clearly shown in the drawing, the intermediate end portions of the coil sections l1 and I8 are grounded at 23 upon the core bar l9, constituting a mid-point ground, since the coil sections l1 and I8 are equal and balanced. The core I!) in turn is grounded at 1 0a.

With the coils l5 and I6 connected with a suitable source of constant voltage current, and with the secondary circuit comprising the coil. sections l1 and I8 open, a suitable exciting current flows through the coils l5 and I6 serving to establish the desired magnetiefield about the core loop, substantially none of the flux under such circumstances traversing the bars H3 or 22. When the secondary circuit comprising the coil sections l1 and I8 is then closed through a neon tube or similarly acting device, an induced current is built up in the secondary circuit and a corre sponding working current flows through the primary circuit, a portion of the magnetic flux being diverted from the portions of the core loop upon which the secondary coil sections are mounted and being caused to flow across the loop through the shunt bar l9 and the air gaps 20 and 2|. Under normal operating conditions, no fiux traverses the bar 22 either when the secondary circuit is open or when it is closed through a suitable work device such as a neon tube. The factors producing a leakage of a definite proportion of the flux across the air gap 20 are precisely duplicated at the opposite side of the instrument for producing an equal leakage across the air gap 2|, and there is no occasion for any of such leakage flux to traverse a path of increased length through the bar 22.

In the normal operation of the device as shown in Fig. 1, the amount of the flux diverted across the air gaps and 2i and through the shunt core bar i9 is controlled by the size of the air gaps, the shunt core bar l9 being of such size as to carry the diverted flux without any saturation therein. The air gaps are made of such aggregate size that when the transformer as a whole is short-cireuited across its terminals such a proportion of the flux is diverted to a leakage path across the air gaps and through the shunt core bar I! from the normal path through the portions of the core upon which the secondary coil sections I1 and I8 are mounted as to limit the current flowing by induction through said coil sections. The induced current through said secondary coil sections under such circumstances is increased as compared with the induced cur rent through said coil sections when the instrument is operating normally under full load conditions, but such increase is kept within certain predetermined limits as may be required for maintaining the selected margin of safety.

As will be appreciated from a study of applicants device, if at any time one of the secondary terminals should become electrically connected with the ground, the corresponding secondary coil section I! or i8 would be short-circuited. This might occur by reason of the breakage of the neon tube, or it might possibly be caused by leakage of the current between the conductor and the casing of the transformer by reason of the presence of moisture or the like. If for example there should be a heavy leakage of current from the secondary lead l8a to the ground,

as indicated by dotted lines at no in Fig. 1, the coil section l8 would be short-circuited through the core. This would leave only the secondary coil section I! effectively connected by the leads Ila and "a with the neon tube, with only half as many turns therein as are normally in use in the two coil sections, with the result that the production of an induced current in said secondary coil section would immediately cease, since the voltage pressure in said one coil alone would not be sufficient for forcing a current through the neon tube. At the same time, the magnetic leakage across the air gap 20 caused normally as a result of the current through the coil section I! would immediately terminate, since the flux would then pass with very little resistance through the portion of the core upon which said secondary coil section I! is mounted. Under these conditions, the auxiliary core bar portion 22 becomes effective for preventing any excessive increase in the current through the coil section l8, the flux pressure produced in the core by the induced current through the coil section I! and the working current through the primary coil sections l5 and i6 causing the diversion of a large proportion of the flux from the core bar portion upon which said coil section I. is mounted to a path across the air gap 2| and thence through a portion of the shunt bar I! and through the auxiliary core bar portion 22. This causes a very substantial decrease in the induced current in said coil section It as compared with the current which would have been induced in said coil section if the shunt core path through the bar portions l9 and 22 had not been provided. The amount of current through the short-circuited coil section I. is, of course, controlled by the size of the air gap 2!, the core bar portions i9 and 22 being of such size in the arrangement shown as to carry the diverted flux without saturation therein. Under such circumstances the increase in the current through the coil section I! when short-circuited by a leakage to ground at lib would be substantially the same as the increase in the current through said coil section when the transformer as a whole is short-circuited across its terminals.

As a result of my improved arrangement, the transformer is fully protected from injury such as would result if no means were provided for effectually limiting the amount of the induced current in the short-circuited coil. My construction is such that no injury would result to the coil or its insulation or to the remaining portions of the transformer even if the transformer should remain in operation for hours with the shortcircuited condition continuing, since the limited increase in the current in the short-circuited coil section would not injure the instrument. In many cases, where the short circuit was caused by moisture conditions the transformer would resume normal operation again for lighting the neon tube as soon as the moisture had escaped by evaporation or otherwise.

In the construction shown in Figs. 3 and 4, the arrangement is similar to that above described, except that a changed form of auxiliary core means is provided. In the arrangement shown in Fig. 3, a. laminated core bar 24 is provided across the core loop between the primary coilsectlons and the secondary coll sections, such bar in the arrangement shown being held in position by means of pieces of fiber 25 at the ends of the bar providing in effect air gaps 25a. In the arrangement shown, an auxiliary core bar 26 is employed corresponding to the bar 22 of the arrangement shown in Fig. l but formed separately from the 'bar 24 and separately from the cross leg portion I4, the bar 26 in the arrangement shown being formed solid rather than laminated as shown in Figs. 1 and 2 and being of reduced cross-sectional size as compared with the shunt bar portion 24.

The operation of the arrangement as shown in Fig. 3 with respect to the safety factor is the same as that above described in connection with Fig. 1, except as to the amount of current flowing under short-circuit conditions. With the shunt core bar 24 of the same cross-sectional size as that of the bar I9 of the Fig. 1 construction, and with the air gaps 25a of the same effective size as that of the air gaps 20 and 2|, the operation of the instrument of Fig. 3 when short-circuited as a whole across its terminals is the same as that above described in connection with the device of Fig. 1, the current under such circumstances being kept within the same limits in the two instruments. When only one of the secondary coil sections ll-IB is short-circuited, however, the operation in connection with the device of Fig. 3 is different from that in connection with the device of Fig. 1. As above stated, the core bar 22 of Fig. 1 is of such size as to prevent a close approach to magnetic saturation therein. The core bar 26 of Fig. 3, however, is of smaller cross-sectional size than that of bar 22, being made of such size as to approach saturation and thus limit the leakage of flux therethrough. The amount of the leakage flux when only one secondary coil section is short-circuited is thus kept below the amount of leakage flux when the transformer as a whole is short-clrcuited, the degree of 'difierence being controlled by the size of the bar 26. As the size of the bar 26 is reduced below the size of the bar 24, the amount of the induced current through a single short-circuited secondary coil section is increased. A reduction in the thickness of the bar 26 transversely of the transformer also provides additional clearance adjacent to the secondary coil sections making possible a reduction in the over-all width of the transformer. I prefer accordingly under some circumstances to make the auxiliary core bar portion 26 as thin as possible consistent with a suitable margin of safety with respect to the current through a single secondary coil section when short-circuited.

I claim:-

1. In a reactance transformer for use with luminous tubes, the combination of a core in the form of a loop; primary coil means on said core; two secondary coil sections on said core connected in series in cooperative relation to each other with their intermediate ends grounded; and auxiliary core means serving to connect across the loop between the primary coil means and said secondary coil sections, with an eiiective air gap in said connection for diverting a portion of the flux from the portions of the loop upon which said secondary coil sections are mounted and thus controlling the strength of current flowing through said secondary coil sections under normal conditions, and serving, by cooperation with portions of said core loop, as connections in shunt relation about said secondary coil sections respectively, with an effective air gap interposed in each of said shunt connections of substantially smaller size than said first mentioned air gap adapted when one of said secondary coil sections is short-circuited to divert a portion of the flux from the portion of the loop upon which said secondary coil section is mounted, for preventing the establishment of a destructive overload current through said secondary coil section.

2. In a reactance transformer for use with luminous tubes, the combination of a core in the form of a loop; primary coil means on said core; two secondary coil sections on said core connected in series in cooperative relation to each other with their intermediate ends grounded to said core loop; and auxiliary core means serving to connect across the loop between the primary coil means and said secondary coil sections, with an effective air gap in said connection for diverting a portion of the flux from the portions'of the loop upon which said secondary coil sections are mounted and thus controlling the strength of current flowing through said secondarycoil sections under normal conditions, and serving, by cooperation with portions of said core loop, as connections in shunt relation about said secondary coil sections respectively, with substantially half of said first mentioned air gap contained in each of said shunt connections whereby when one of said secondary coil sections is short-circuited through the core the shunt connection about said secondary coil section diverts a portion of the flux from the portion of the loop upon which said secondary coil section is mounted for preventing the establishment of a destructive overload current through said secondary coil section.

3. In a reactance transformer for use with luminous tubes, the combination of a core in the form of a loop; primary coil sections on oppositely disposed legs of said core loop and connected in cooperative relation to each other; secondary coil sections on said legs in end to end relation to said primary coil sections respectively and connected in series in cooperative relation to each other with their mid-point portion grounded; and auxiliary core means serving, by cooperation with portions of said core loop, as connections in shunt relation about said secondary coil sections respectively, with substantially equalized air gaps interposed in said shunt connections, and serving to connect across the core loop between the primary coil sections and said secondary coil sections, with both of said air gaps interposed in said last named connection.

4. In a reactance transformer for use with luminous tubes, the combination of a core in the form of a loop; primary coil sections on 0ppositely disposed legs of said core loop; secondary coil sections on said legs in end to end relation to said primary coil sections respectively and connected in series in cooperative relation to each other; and auxiliary core means connected with the cross leg of said core loop at a point between said secondary coil sections and extending about said secondary coil sections respectively in shunt relation thereto, with an air gap in each of said shunt connections, and serving as a connection across the core loop between the primary coils and the secondary coils, with a substantially greater effective air gap therein than either of said first named air gaps.

5. In a reactance transformer for use with luminous tubes, the combination of a core in the form of a loop; primary coil sections on oppositely disposed legs of said core loop; secondary coil sections on said legs in end to end relation to said primary coil sections respectively and connected in series in cooperative relation to each other with their intermediate end portions grounded; an auxiliary core bar extending across said core loop with an air gap at each end thereof for diverting a portion of the flux normally from the portions of the core loop upon which said secondary coil sections are mounted and thus controlling the strength of current flowing through said secondary coil sections; and other auxiliary core means extending from said auxiliary core bar into engagement with the cross leg of the core loop between said secondary coil sections, adapted, when one of said secondary coil sections is short-circuited, to divert a portion of the flux from the portion of the core loop upon which said secondary coil section is mounted, for preventing the establishment of a destructive overload current through said secondary coil section,

6. In a reactance transformer for use with luminous tubes, the combination of a core in the form of a loop; primary coil sections on oppositely disposed legs of said core loop; secondary coil sections on said legs in end to end relation to said primary coil sections respectively and connected in series in cooperative relation to each other, with their intermediate end portions grounded to said core loop; an auxiliary core bar extending across said core loop between the primary coil sections and the secondary coil sections, with two air gaps interposed therein in spaced relation; and other auxiliary core means extending from said auxiliary core bar, at a point between said air gaps, to the cross leg of the core loop between said secondary coil sections and formed integrally with both of said parts, adapted, when one of said secondary coil sections is short-circuited through the core, to

divert a portion of the flux from the portion of V winding.

msry and secondary windinss. lid core includin: on H-shlped portion the upper portion of thelezsandtheboroi whichlmelylinkone coilsectionotsaidsecondarywindin nndthc lower portions of the less and bar of which lonely link the other coil section of said leoondlry JOSEPH G. BOLA. 

